The invention relates to a mobile communications system employing a so-called multi-numbering scheme, i.e. different subscriber numbers for different teleservices of the subscriber.
In addition to conventional data transmission, modern mobile communications systems provide the subscribers with a variety of data transfer features. The services provided by the mobile communications systems may generally be divided into Teleservices and Bearer Services. A bearer service is a telecommunication service that allows transmission of signals between user-network interfaces. An example of bearer services are modem services. In a teleservice, the network also provides terminal equipment services. Examples of major teleservices, in turn, are speech, telefax and videotext services.
One mobile subscriber may typically have a right to different teleservices and bearer services, which are herein generally referred to as basic services. The subscriber may have an access e.g. to speech, telefax and data services. A mobile-terminating or mobile-originating call may thus require any of these basic services, for which reason the correct service must be addressed to the mobile communications network. E.g in the pan-European GSM mobile communications system GSM, call set-up signalling transmitted by a mobile station contains information on the required basic service in a specific Bearer Capability Information Element BCIE. The mobile network may thus choose the appropriate basic service for the mobile-originating calls. Calls received from an ISDN (Integrated Services Data Network) also contain a similar information element that indicates the service required. In case a call originates from or is routed via the public switched telephone network (PSTN), however, information on the type of the call will not be transmitted to the mobile communications network. In such a case, the network should be informed some other way which basic service the call requires.
A prior art solution to the above problem is a Multinumbering Scheme, in which a mobile subscriber has a number of directory numbers corresponding to the number of services to which he wishes to receive incoming calls. A directory number is also termed as a Mobile Subscriber ISDN Number (MSISDN). A subscriber may have a directory number e.g. for a speech service, a telefax service and a modem service. In accordance with the Multinumbering Scheme, a calling subscriber dials the directory number of the mobile subscriber according to the desired service. In the pan-European mobile communications network, the services of the subscribers are determined in a subscriber's home location register HLR, in which other subscriber information is also stored permanently. The HLR is also used for storing information on the mapping between the directory numbers and the services of the subscriber. In the HLR, a specific BCIE element indicating the type of a call and the network resources required for the call is also linked with the directory number (MSISDN). A BCIE is described e.g. in GSM Recommendation 04.08, version 4.5.0, pp. 423-431. The HLR also contains an IMSI (International Mobile Subscriber Identity) which is used within the GSM network. A mobile subscriber has only one IMSI, which is common to all the basic services.
The GSM system also has another location register, a visitor location register VLR, into which part of the subscriber data stored in the HLR is copied when the subscriber is located within the area of the VLR.
FIG. 2 illustrates call set-up of a mobile-terminating call in the GSM mobile communications system employing a multinumbering scheme. In step 1, the call arrives at the first gateway MSC (GMSC) of the network. The GMSC will send a routing information request (message 2) to the HLR of the subscriber, said HLR being determined on the basis of the directory number MSISDN of the subscriber. Along with the routing information request message 2, the MSISDN of the subscriber (and possibly ISDN BCIE+HLC+LLC) is also transmitted. In connection with a location updating, the information on the VLR in whose area the subscriber is located has been updated in the HLR of the subscriber. On the basis of that information, the HLR will transmit to the VLR a roaming number request (message 3). Along with the roaming number request, the VLR will also be provided with the IMSI of the mobile subscriber and the BCIE related to the called MSISDN (or an ISDN BCIE received along with message 2). The BCIE indicates e.g. the network resources required by the call, but not directly the type of the basic service. The VLR will store the BCIE it has received and allocate a Mobile Station Roaming Number MSRN. The VLR will transmit the allocated roaming number to the HLR along with an response message 5. The HLR, in turn, will forward the roaming number to the GMSC that has requested the routing information in a message 6. The roaming number space has been determined so that it will route the call every time to the MSC whose VLR has allocated the roaming number. The GMSC may thus route the call further on the basis of the roaming number MSRN by transmitting an initial address message 7 to the mobile services switching centre MSC indicated by the roaming number.
After receiving the initial address message 7, the MSC will detect in a roaming number analysis that the call is terminating within the area of the same MSC, and it is not intended to be routed further. The MSC will thus request call set-up information on the called subscriber from its own VLR (message 8). The VLR will normally return the information required in the response message 9, said information containing e.g. the BCIE. Provided that the MSC is able to provide the data transmission resources required by the BCIE, call set-up signalling will be carried out between the MSC and the MS. The signalling is illustrated with arrows 10 and 11.
A supplementary service provided by the mobile communications systems is call forwarding, which may be activated by the subscriber. Call forwarding may be call forwarding unconditional, in which case a call is forwarded to a given new number every time. Call forwardings of this kind are usually carried out by the HLR. Call forwarding may be determined to take place conditionally, that is, in case the subscriber is busy, the subscriber does not answer or the subscriber is not available. For call forwarding procedures of this kind, information on the status of the subscriber (available/busy) or progressing of the call set-up is required, and they are therefore carried out by the VLR/MSC.
With reference to FIG. 3, let us study a call set-up procedure of a mobile-terminating call, associated with call forwarding conditional in the mobile services switching centre MSC serving the mobile station. In FIG. 3, the call set-up messages and steps 1, 2, 3, 4, 5, 6, 7 and 8 are completely similar to those explained above in connection with FIG. 2. When the VLR receives a subscriber data request 8 from the MSC in the case shown in FIG. 3, the VLR will detect e.g. that the mobile station is busy. The VLR will then check from the subscriber data whether the mobile station has activated call forwarding conditional in case the subscriber is busy. The VLR will detect that the subscriber has call forwarding conditional to a specific call forwarding number, and transmit to the MSC an response message 9, in which the MSC is commanded to forward the call to the number provided. Along with signalling related to call forwarding, an Original Called Number OCD and a Redirecting Number will also be forwarded. In some types of signalling, only one number is transmitted, in which case the number is the Redirecting number.
In a system in accordance with the GSM Recommendations, only a MSISDN in accordance with a Primary Service, a Primary MSISDN, is transmitted from the HLR to the VLR, although a multinumbering scheme would be in use. The primary MSISDN is usually the MSISDN of the speech service. For this reason, the Primary MSISDN, usually a speech MSISDN, is also transmitted as a redirecting number and an OCD indication in call forwarding, although the call to be forwarded would have been received e.g. to the MSISDN number of the telefax service.
A similar problem also arises in connection with mobile-originating calls. The MSC transmits the called subscriber the call set-up message of the MSISDN number of the calling subscriber in a Calling Line Identity (CLI) field of the calling subscriber. Since the MSC receives the MSISDN number from the VLR, the CLI is presently represented by the MSISDN, usually the speech MSISDN, of the primary service every time, although the call would be a telefax call. There are automatic call-back telefax terminals, which call back to the number of the calling subscriber in case the telefax has been busy when it has been called. The call will take place on the basis of the identity CLI of the calling subscriber. When the CLI of the calling telefax terminal is now a speech MSISDN, the called telefax terminal will make a call to that speech MSISDN, and the mobile network will establish a speech call instead of a telefax call.